1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device for controlling an angle at which an image is viewed, and a driving method thereof.
2. Description of the Related Art
A general LCD device controls light transmittance of liquid crystal (LC) according to video data to display images corresponding to the video data. Since an LC panel, which is a primary element of an LCD device, displays an image using external light, an angle (i.e., a viewing angle) at which the image is viewed by a user is inevitably limited. To increase the limited viewing angle of the LC panel, a method of applying a horizontal electric field, a method using a compensation film, and a multiple division mode method using an opening pattern or a protrusion on a transparent electrode are introduced to the LC panel. This transverse electric field driving method, the compensation film method, and the multiple division mode method allow the LC panel to secure a sufficient viewing angle.
Recently, users of portable terminals such as portable phones, personal digital assistants (PDAs), and computers have demands for preventing date from being viewed by other persons while the users use the portable terminals. LCD devices used as display devices of the portable terminals are requested to support both a narrow viewing angle mode as well a wide viewing angle mode, reflecting confidentiality maintenance and security requests.
As an alternative for meeting multiple viewing angle modes, a double structure LC panel has been proposed. As illustrated in FIG. 1, the double structure LC panel includes a normal panel 10 used for displaying an image and an interference panel 12 located on the normal panel 10. The normal panel 10 is used for displaying an image, while the interference panel 12 allows light propagating to a lateral direction of the panel for interference. As described above, the double structure LC panel realizes switching of a viewing angle mode for an image using light interference caused by the interference panel 12.
A viewing angle controllable LCD device including a double structure LC panel selectively drives the interference panel 12 to realize a wide viewing angle mode and a narrow viewing angle mode. In other words, the LCD device turns on or off the interference panel 12 depending on a viewing angle mode. Since external light has to pass through a double LC layer in the above-described double structure LC panel, brightness of an image considerably decreases. In addition, the thickness and weight of the double structure LC panel also increases.
As an alternative for improving a double structure LC panel that can control a viewing angle, a single layer structure LC panel that can control a viewing angle including interference cells installed to form one side (or the same layer) together with color pixels has been proposed. The single layer structure LC panel that can control the viewing angle has an advantage of displaying an image without brightness reduction and can be made in a slim profile. Accordingly, this LCD device allows image data not to be viewed by other persons using the single layer structure LC panel that can control the viewing angle.
Recently, image data to be displayed by a display device frequently include data partially requiring security depending on characteristic and attribute of the data. In addition, data requiring security can be included in image data in view of business characteristics or personal situation. Accordingly, a viewing angle controllable LCD device needs to display image data so that security of a portion of the image data can be maintained according to a user's request.